1. Field of the Invention
This invention relates to externally fired combined cycle gas turbine systems which are sometimes referred to as EFGT Systems.
2. Background of the Invention
Externally fired gas turbine/combined cycle systems have been described in the literature for a number of years. Such systems include a compressor for compressing ambient air, an indirect contact heat exchanger in which combustible products, e.g., gas and/or fuel vapors, hereinafter referred to as xe2x80x9ccombustible gasesxe2x80x9d, are burned to heat the compressed air, and a turbine in which the heated compressed air is expanded driving a generator that produces electricity. Heat contained in the turbine exhaust is used to vaporize water that is converted into steam in a separate water-based, closed Rankine cycle power plant, the steam being expanded in a steam turbine in the power plant for driving a generator that produces additional electricity.
EFGT systems have been proposed for use with low calorific, unclean gaseous fuels as well as with hot gaseous fuels. Solid fuels are more difficult to incorporate into EFGT systems because of the problems associated with ash and noxious gases produced during the combustion process. It is therefore an object of the present invention to provide a new and improved externally energized gas turbine system such as an externally fired combined cycle gas turbine system which is capable of using solid fuels without many of the usual attendant problems associated with burning such fuel in a combined cycle gas turbine system.
An externally energized gas turbine system such as an externally fired gas turbine system according to the present invention has a compressor for compressing ambient air and producing compressed air, an air heat exchanger for heating the compressed air to produce heated compressed air, a turbine for expanding the heated compressed air to produce expanded air, and a generator connected to the turbine for generating electricity. According to the present invention, the system also preferably includes what is termed xe2x80x9ccombustible products producing apparatusxe2x80x9d for processing fuel to produce gas and/or fuel vapor collectively referred to hereinafter as xe2x80x9ccombustible gasesxe2x80x9d, and an external combustion chamber for burning the combustible gases and transferring heat to the compressed air flowing through the air heat exchanger and producing heat depleted combustion products. The system also preferably includes a closed Rankine cycle steam power plant having a water heat exchanger for vaporizing water and producing steam using heat contained in the gaseous heat depleted combustion products. The power plant further includes a steam turbine for expanding the steam thereby producing power, and from which expanded steam exits, and a steam condenser for condensing the expanded steam producing condensate that is returned to the water heat exchanger.
In one embodiment of the invention, the water heat exchanger includes a preheater heated by the expanded air for heating the condensate and producing preheated water, and a vaporizer heated by the heat depleted combustion products for vaporizing the preheated water thereby producing steam for the turbine of the power plant.
In a preferred form of the invention, the combustible products producing apparatus includes a pyrolyzer for processing oil shale and producing combustible gases and a carbonaceous residue, and an air furnace for combusting the organic material remaining in the carbonaceous residue thereby producing hot flue gases and ash in the form of hot particulate. Means are provided for returning hot ash to the pyrolyzer. In this instance, the combustible gases produced by the pyrolyzer and the hot flue gases produced by the air furnace, together with solid particulate matter, constitute the combustible products produced by the processing of the oil shale by the combustible products producing apparatus.
In another embodiment of the invention, the water heat exchanger includes a superheater heated by the flue gases for superheating steam produced by the vaporizer. In another embodiment of the invention, the water heat exchanger includes a preheater heated by both the heat depleted combustion products and the expanded air (for heating the condensate thereby producing preheated water), and a vaporizer heated by the flue gases for vaporizing the preheated water.
In a further embodiment of the invention, the water heat exchanger includes a vaporizer heated by both the heat depleted combustion products and the expanded air for converting the condensate into steam. In such case, a second water-based, closed loop Rankine cycle power plant may be provided. The second power plant has a second water heat exchanger for vaporizing water and producing steam using heat contained in the flue gases produced by the gas producing apparatus, and a second steam turbine for expanding the steam and producing power and expanded steam. The second power plant also includes a second steam condenser for condensing the expanded steam exiting the steam turbine and producing condensate which is returned to the second water heat exchanger.
In a still further embodiment, heat depleted combustion products and expanded air heat an organic fluid in an organic fluid vaporizer producing organic vapor for operating an organic vapor turbine. In such case, the flue gases produced by the combustible products producing apparatus heat water in a water heat exchanger for vaporizing the water and producing steam for operating a steam turbine.
The organic vapor is supplied to the organic vapor turbine for producing power. Expanded organic vapor exits from the organic vapor turbine and is supplied to a condenser for producing organic fluid condensate. Steam produced in the water heat exchanger is supplied to the steam turbine for producing power. Expanded steam exhausted from the steam turbine is supplied to a steam condenser for producing steam condensate. In this embodiment, the expanded steam supplied to the steam condenser is cooled by organic fluid condensate and the resultant steam condensate is supplied to the water heat exchanger. Organic fluid condensate supplied to the steam condenser is thus preheated and then supplied to the organic fluid vaporizer. A second Rankine cycle organic fluid power plant is also included in this embodiment, the organic fluid being vaporized by heat extracted using an interstage cooler associated with the air compressor of the gas turbine. In the second Rankine cycle organic fluid power plant, organic vapor produced by cooling the interstage cooler is supplied to a second organic vapor turbine for producing power. Expanded organic vapor exhausted from the second organic vapor turbine is supplied to a condenser for producing organic fluid condensate which is supplied by a circulation pump to the interstage cooler.